Design of ultrastrong but ductile medium-entropy alloy with controlled precipitations and heterogeneous grain structures

By Wanpeng Li, T. Chou, Tao Yang, W. Chuang, Jacob C. Huang, J. Luan, Xiangkai Zhang, X. Huo, H. Kong, Quanfeng He and 3 more. 2021

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Abstract In this study, we develop a non-equiatomic Co2CrNi1.5Al0.25Ti0.25 quinary medium-entropy alloy (MEA). The heterogeneous grain structure (HGS) (comprising residual deformed grains, micro-sized recrystallized grains and nano-sized recrystallized grains) and heterogeneous precipitation (HP) of the L12 phase corresponding to different kinds of grain structures are simultaneously introduced into the alloy by the well-designed thermomechanical processing. The alloy exhibits an ultra-high yield stress ( σ y ) of 1.73 GPa, ultimate tensile stress ( σ u ) of 1.89 GPa and remarkable total elongation ( e te ) up to 16.0% at 293 K, as well as ultra-high σ y up to 2.02 GPa, σ u up to 2.31 GPa and excellent e te up to 21.2% at 77 K. The synergy of multiple hardening mechanisms, mainly including back-stress hardening, precipitation hardening and pre-existed dislocation hardening contributes to the ultra-high σ y at 293 K and 77 K. The HGS promotes the continuously increased geometrically necessary dislocations (GNDs) density, which, combined with the nano-spaced stacking fault (SF) networks, leads to the outstanding three-stage work-hardening behaviors during tensile tests at 293 K and 77 K. The simultaneous introduction of HGS and HP into this newly-developed MEA without brittle intermetallic phase, is a new effective method in designing high-performance alloys applied at both ambient and cryogenic temperatures.

Subfields: Aerospace Engineering, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/9ee3139df9c3ea9f977fd54096e821a1b97ff7a8